The present invention relates to a magnetic guide of the type comprising an upper U-shaped member forming a running channel for a conveyor chain. In this type of guide the U-shaped member is assembled on a base member forming a fixed structure of the conveyor system.
In the prior art it was proposed to insert magnets in seats in the U-shaped member to hold the chain in position and entirely or partly made of ferromagnetic material. In this manner the problem arose of how to receive and hold the magnets in the U-shaped member.
Depending on their position on the U-shaped member there have been proposed various solutions for the closing of the seats. For example, EP 0,325,333 describes solutions for closing the seats when they face the central channel of the U-shaped member.
EP 0,159,074 describes guides with magnet seats which open on the lower face of the U-shaped member and are closed by purposeful strips of flexible material. To seek to hold the magnets steady in the seats, elastic buffers, for example of rubber, are arranged between the strips and the magnets.
Insertion of the magnets in seats in the U-shaped member permits holding the distance between the magnets and the ferromagnetic parts of the chain smaller. But it must be considered that the U-shaped member is subject to wear and must therefore be replaced periodically by disassembling it from the base member. The U-shaped member with seats and magnets fixed in them is however a relatively costly assembly. On the other hand disassembly of the individual magnets from the worn member and their transfer to the new U-shaped member is a long and costly operation. Even if they are not reused the magnets must be disassembled from the U-shaped member to perform differentiated refuse elimination.
Since insertion of the magnets one by one in the seats is an operation requiring much time and it is made difficult by the force of attraction between the magnets themselves there has also been proposed in EP 0,447,696 to provide a single elongated member in which are enclosed all the magnets of one side of the guide. The magnets can be introduced this way in the U-shaped member by a single operation. This facilitates both initial assembly and transfer of the magnets from a worn U-shaped member to a new one while making the operation of replacement of the worn U-shaped members more economical.
In EP A 0,775,649 is proposed providing a guide with U-shaped member having cavities for the magnets which are open below and magnets fixed on the base member instead of on the U-shaped member. In this manner the U-shaped member becomes a `cap` which receives the magnets only upon complete assembly of the guide. This permits disassembly of the U-shaped member only, for example for replacing it when it is worn, while leaving the magnets in their position on the base. The U-shaped member not incorporating the magnets costs less and is easier to replace. Nevertheless the cost of machining necessary to provide the seats therein remains high. In addition the material of the U-shaped members high-strength and costly in itself since it must have high wear resistance and low friction and the `cap` solution necessitates a relatively high quantity of material to produce the U-shaped member. In addition, when the U-shaped member is removed the magnets remain completely exposed with the risk of accidental blows capable of breaking of removing them. The general purpose of the present invention is to obviate the above mentioned shortcomings by making available a magnetic guide for chain conveyors which would have an excellent magnetic attraction characteristic and an economical and replaceable U-shaped member without compromising easy running of the chain and durability of the parts subject to wear.